1. Field of the Invention
The present invention relates to the identification and use of diagnostic markers for acute ischemic stroke. In a various aspects, the invention relates to methods for rapid and early detection of acute ischemic stroke, as well as the identification of individuals at risk for acute ischemic stroke.
2. Background
Stroke is clinically defined as a rapidly developing syndrome of vascular origin that manifests itself in focal loss of cerebral function. In more severe situations, the loss of cerebral function is global. Stroke can be categorized into two broad types, “ischemic stroke” (about 87%) and “hemorrhagic stroke” (about 10%). Ischemic stroke occurs when the blood supply to the brain is suddenly interrupted. Hemorrhagic stroke happens when a blood vessel located in our around the brain bursts leading to the leakage and accumulation of blood directly in the brain tissue. Additionally, a patient may experience transient ischemic attacks, which indicates a high risk for the future development of a more severe episode. Stroke also includes subarachnoid hemorrhage (about 3%).
The symptoms of stroke often include numbness or weakness, especially on one side of the body; sudden confusion or trouble speaking or understanding speech; sudden trouble seeing in one or both eyes; sudden trouble walking; dizziness; or loss of balance or coordination. Stroke is the most common devastating neurologic disease in the world and despite recent progress understanding stroke mechanisms, stroke management is still not optimal.
Stroke is the third leading cause of death in the world, after only heart disease and cancer. In the United States alone, approximately 780,000 people experience a stroke each year, which contributes to an overall financial burden of over $65 billion per year. As noted, ischemic stroke accounts for most instances of stroke in patients, and consequently, the category of stroke having the greatest financial burden.
Ischemic stroke encompasses thrombotic, embolic, lacunar and hypoperfusion types of strokes. Thrombi are occlusions of arteries created in situ within the brain, while emboli are occlusions caused by material from a distant source, such as the heart and major vessels, often dislodged due to myocardial infarct or atrial fibrillation. Less frequently, thrombi may also result from vascular inflammation due to disorders such as meningitis. Thrombi or emboli can result from atherosclerosis or other disorders, for example, arteritis, and lead to physical obstruction of arterial blood supply to the brain. Lacunar stroke refers to an infarct within non-cortical regions of the brain. Hypoperfusion embodies diffuse injury caused by non-localized cerebral ischemia, typically caused by myocardial infarction and arrhythmia.
Of the 88% of ischemic strokes that occur each year, 8-12% results in death within 30 days. The risk of ischemic stroke is associated with various familial and environmental factors, such as the presence of hypertension, obesity, tobacco use, and a positive family history. Determinants of outcome include non-modifiable risk factors such as age, race, gender and genetic variation along with clinical phenotypes of severity, such as stroke scale score, the presence of fever and serologic blood markers. Advances in neuroimaging and acute clinical management have resulted in greater numbers of patients surviving the initial insult. However, morbidity remains high secondary to complications following the primary event and initial misdiagnosis.
The onset of ischemic stroke is often abrupt, and can begin with a manifestation of neurologic deficits that worsen over a 24-48 hour period. Stroke-associated symptoms commonly include unilateral neurologic dysfunction that extends progressively, without producing headache or fever. Early manifestations may rapidly progress to more severe symptoms within a few minutes.
Hemorrhagic stroke is caused by intracerebral or subarachnoid hemorrhage, i.e., bleeding into brain tissue, following blood vessel rupture within the brain. Intracerebral and subarachnoid hemorrhage are subsets of a broader category of hemorrhage referred to as intracranial hemorrhage. Intracerebral hemorrhage is typically due to chronic hypertension, and a resulting rupture of an arteriosclerotic vessel. Stroke-associated symptom(s) of intracerebral hemorrhage are abrupt, with the onset of headache and steadily increasing neurological deficits. Nausea, vomiting, delirium, seizures and loss of consciousness are additional common stroke-associated symptoms.
In contrast, most subarachnoid hemorrhage is caused by head trauma or aneurysm rupture which is accompanied by high blood pressure release which also causes direct cellular trauma. Prior to rupture, aneurysms may be asymptomatic, or occasionally associated with tension or migraine headaches. However, headache typically becomes acute and severe upon rupture, and may be accompanied by varying degrees of neurological deficit, vomiting, dizziness, and altered pulse and respiratory rates.
Transient ischemic attacks (TIAs) have a sudden onset and brief duration, typically 2-30 minutes. Most TIAs are due to emboli from atherosclerotic plaques, often originating in the arteries of the neck, and can result from brief interruptions of blood flow. The symptoms of TIAs are identical to those of stroke, but are only transient. Concomitant with underlying risk factors, patients experiencing TIAs are at a markedly increased risk for stroke.
There are few pharmaceutical therapies for treating stroke. In point of fact, the only Food and Drug Administration (FDA) approved treatment for ischemic stroke is recombinant issue plasminogen activator (rtPA), alteplase. Multiple attempts to identify other pharmacologic agents have resulted in negative findings; therefore a redirection of the science is necessary to understand the human variable response to stroke, in particular, to ischemic stroke, to provide alternative avenues for therapeutic treatment.
Since its commencement into the clinical arena in 1996, recombinant tissue plasminogen activator (rtPA) has proven to be a promising therapeutic treatment for ischemic stroke and is safe and effective for use in routine clinical practice. However, its powerful effects are not seen without significant clinical complications. In addition, rtPA is only approved for use when patients present to the hospital within three hours from onset of symptoms. The downside is that the median time from stroke symptom onset to presentation to the emergency department is 3-6 hours. A recent study addressed the possibility of extending this limited therapeutic time window and it was shown that intravenous rtPA given between 3 and 4.5 hours after onset of symptoms significantly improved clinical outcomes following ischemic stroke compared to placebo. This is promising given that the time window limit of 3 hours and a large list of contraindicating factors for thrombolytic therapy currently results in only 3-8% of stroke patients receiving rtPA.
The advancements of rtPA therapy aside, there is still a demand for alternative acute ischemic stroke therapies in clinical practice. Unfortunately, the results of recent clinical trials have demonstrated that there is still a gap in the understanding of the variable human response to ischemic stroke. Numerous promising pre-clinical therapeutics display insignificant clinical utility in human patients, which speaks to the difficulty of translating what is learned at the bench to the patient at the bedside.
These negative findings may be due in part to the complexity of the human physiologic response to ischemic stroke, limited knowledge about the multiple pathways interacting in response to ischemic stroke and the implications of genomic variability on individual recovery from ischemic stroke. The difficulty may also be attributable to insufficient classification of ischemic stroke subtype. It is possible that gene expression profiling can help to identify subtypes of ischemic stroke, which has tremendous utility in designing therapeutic strategies for treatment. A better understanding of stroke pathophysiology in humans and more appropriate stroke subtyping may provide the foundation needed to design appropriate therapeutics for battling ischemic stroke and other stroke types.
Immediate diagnosis and care of a patient experiencing stroke can be critical. As noted, tissue plasminogen activator (rtPA) given within three hours of symptom onset in ischemic stroke is beneficial for selected acute ischemic stroke patients. Patients may also benefit from anticoagulants (e.g., heparin) if they are not candidates for rtPA therapy. In contrast, thrombolytics and anticoagulants are strongly contraindicated in hemorrhagic strokes. Thus, early and rapid differentiation of ischemic stroke from hemorrhagic-type stroke is imperative and often critical. Delays in the confirmation of stroke diagnosis and the identification of stroke type limit the number of patients that may benefit from early intervention therapy.
Another limitation in the diagnosis of ischemic stroke relates to the fact that, due to the rapidity of onset and progression of acute ischemic stroke, circumstances are such that ischemic stroke patients are often not seen by clinicians having the appropriate knowledge and training to be able to provide a correct, life-saving diagnosis. For instance, brain imaging technology is an integral and key aspect of the clinical stroke evaluations. However, such technology is often not available. Even if the technology is available, proper interpretation of brain imaging results concerning stroke diagnoses is best suited for those clinicians who are highly and specifically trained in the treatment and care of stroke patients. Indeed, due to the rapid onset of an acute ischemic stroke and other factors, such as the scarcity of trained stroke-clinicians and neurologists, clinical assessment of a potential victim is often carried out by a non-stroke specialist, e.g., a family practitioner, paramedic or triage nurse. Thus, achieving and accurate and rapid early diagnosis is often not possible under present clinical circumstances.
Patients, even those with mild symptoms, may be eligible for various ischemic stroke therapies if they can be started within a few hours of symptom onset. Patients who do not receive such early therapies are at an increased risk of recurrent stroke, often occurring even within a matter of days. Thus, prompt administration of a suitable therapy in a timely manner can substantially increase the efficacy of treatment while reducing the risk of recurrent stroke.
However, presently there are no rapid diagnostic procedures or methods that can be used to reliably determine whether a patient has suffered a stroke, in particular, an acute ischemic stroke, or whether a subject is at risk for ischemic stroke.
Accordingly, a rapid diagnostic test capable of making an accurate clinical diagnosis of ischemic stroke irrespective of the clinician's level of stroke expertise or lack thereof would be extremely useful. To date, the identification of appropriate biomarkers for ischemic stroke have proven to be extremely difficult. This may be tied, in part, to the observation that the proteins associated with stroke-affected brain and neurological tissues are slow to be released into the blood due to the blood-brain barrier. In addition, many potential stroke markers, including markers of cerebral ischemia and inflammation, located in the blood are associated with other conditions that may mimic stroke, e.g., severe myocardial infarction and brain infection.
This invention solves these deficiencies in the art.